Bug 1526514 [wpt PR 15203] - Update wpt metadata, a=testonly

wpt-pr: 15203
wpt-type: metadata

testing/web-platform/meta/portals/portals-host-hidden-after-activation.html.ini

@@ -0,0 +1,5 @@
+[portals-host-hidden-after-activation.html]
+  expected: TIMEOUT
+  [window.portalHost should be null after portal is activated]
+    expected: TIMEOUT
+